When the device boots, you’ll probably notice that everything is very small. There are two variables that set the content scaling for Unity 8 and Ubuntu Touch applications: GRID_UNIT_PX and QTWEBKIT_DPR.

There are also some other options available that may be useful for you depending on your device’s form factor. These are discussed below.

All of these settings are guessed by Unity 8 if none are set. There are many cases, however, where the guess is wrong (for example, very high resolution phone displays will be identified as desktop computers). To manually set a value for these variables, simply create a file at /etc/ubuntu-session.d/[codename].conf specifying them. For example, this is the file for the Nexus 7 tablet:

GRID_UNIT_PX (Pixels per Grid Unit or Px/GU) is specific to each device. Its goal is to make the user interface of the system and its applications the same perceived size regardless of the device they are displayed on. It is primarily dependent on the pixel density of the device’s screen and the distance to the screen the user is at. The latter value cannot be automatically detected and is based on heuristics. We assume that tablets and laptops are the same distance and that they are held at 1.235 times the distance phones tend to be held at.

QTWEBKIT_DPR sets the display scaling for the Oxide web engine, so changes to this value will affect the scale of the browser and webapps.

A reference device has been chosen from which we derive the values for all other devices. The reference device is a laptop with a 120ppi screen. However, there is no exact formula since these options are set for perceived size rather than physical size. Here are some values for other devices so you may derive the correct one for yours:

Device

Resolution

Display Size

PPI

Px/GU

QtWebKit DPR

‘Normal’ density laptop

N/A

N/A

96-150

8

1.0

ASUS Nexus 7

1280x800

7”

216

12

2.0

‘High’ density laptop

N/A

N/A

150-250

16

1.5

Samsung Galaxy Nexus

1280x720

4.65”

316

18

2.0

LG Nexus 4

1280x768

4.7”

320

18

2.0

Samsung Nexus 10

2560x1600

10.1”

299

20

2.0

Fairphone 2

1080x1920

5”

440

23

2.5

LG Nexus 5

1080x1920

4.95”

445

23

2.5

Experiment with a few values to find one that feels good when compared to the Ubuntu Touch experience on other devices. If you are unsure of which is the best, share some pictures (including some object for scale) along with the device specs with us.

FORM_FACTOR specifies the device’s form factor. This value is set as the device’s Chassis, which you can find by running hostnamectl. The acceptable values are handset, tablet, laptop and desktop. Apps such as the gallery use this information to change their functionality. For more information on the Chassis, see the freedesktop.org hostnamed specification.

NATIVE_ORIENTATION sets the display orientation for the device’s built-in screen. This value is used whenever autorotation isn’t working correctly or when an app wishes to be locked to the device’s native orientation. Acceptable values are landscape, which is normally used for tablets, laptops, and desktops; and portrait, which is usually used for phone handsets.

If you have any errors while performing these steps, check see if any of the following suggestions match what you are seeing. If you have completed these steps successfully, congratulations! You’ve reached the end of the porting guide for now. Try to check the functionality of your device by following the Smoke Testing information in Quality Assurance.